[improve][test] Add integration tests for the Debezium SQL Server source connector

## Current state

`debezium/mssql` has **zero tests** — the `DebeziumMsSqlSource` connector is not exercised at all in CI.

## Proposal

Add a Testcontainers-based integration test following the existing pattern in `debezium/mysql` (`DebeziumMysqlSourceTest`): start an `MSSQLServerContainer` with the SQL Server Agent enabled (`MSSQL_AGENT_ENABLED=true`, required for CDC capture jobs), enable CDC on the test database and table (`sys.sp_cdc_enable_db` / `sys.sp_cdc_enable_table`), plus a `PulsarContainer` for schema history, and assert the initial snapshot produces CDC records.

Requires adding a `testcontainers-mssqlserver` entry to the version catalog (resolves via the existing Testcontainers BOM).

_Part of an integration-test coverage sweep of all connector modules._

Start with debezium/mysql/DebeziumMysqlSourceTest and compare it with the DebeziumMsSqlSource connector under debezium/mssql. Review the version catalog entry needed for testcontainers-mssqlserver, then set up the MSSQLServerContainer, CDC configuration, and PulsarContainer as described. Done means CI runs the integration test and the initial snapshot produces CDC records.

Written by the indexing model from the issue text.